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Over the last few decades, the number of diagnostic and therapeutic procedures that involve ionizing radiation has steadily risenparticularly in the modern catheterization laboratory. Given that the cath lab has been dubbed the 'epicenter' of a radiological tsunami, the authors of one study in a mini-focus issue of JACC: Cardiovascular Interventions noted that the cardiology community "bears the responsibility of minimizing radiation exposure" to their patients, themselves, and their professional staff. Two studies examine modifiable factors that could potentially achieve that goal for patients and operators: beam angulation and lower-rate fluoroscopy.

Radiation Air Kerma and Beam Angulation
An important determinant of radiation dose in the cath lab, radiation scatter is governed by several factors including beam orientation and movement. However, according to Shikhar Agarwal, MD, MPH, from the Cleveland Clinic, and colleagues, data detailing radiation dose with modern digital equipment in real-world patient settings do not presently exist. To examine the current-day relationship between beam angulation and radiation scatter, Dr. Agarwal's group extracted prospectively-captured radiation data from a database of 1,975 diagnostic catheterizations (DC) and 755 percutaneous coronary interventions (PCI), which amounted to 138,342 fluoroscopic and 35,440 acquisition ("cine") sequences.

Fluoroscopy and acquisition modes were categorized into tertiles based on the total air kerma measured at a standard reference point. Median duration and air kerma during DC and PCI were significantly different (TABLE). Additionally, the relative proportions of fluoroscopy versus acquisition demonstrated key variances: acquisition contributed more of the total x-ray duration (11.7% vs. 6.0%; p < 0.001) and air kerma (60.3% vs. 33.7%;
p < 0.001) during DCs than PCIs.

TABLE. Comparison of Radiation Time and Radiation Air Kerma*

DCs (n = 1,975)

PCIs (n = 755)

Radiation time

Total x-ray time (seconds)

428 (260745)

1,382 (9102,147)

Fluoroscopy time

seconds

380 (215679)

1,299 (8282,029)

% of total time

88.3 (82.292.6)

94.0 (91.696.2)

Acquisition time

seconds

49 (3964)

84 (64109)

% of total time

11.7 (7.417.8)

6.0 (3.88.4)

Radiation dose

Total air kerma (mGy)

677.2 (447.61,060.9)

2,188.3 (1,356.93,565.2)

Fluoroscopy air kerma

mGy

250.5 (138.2492.8)

1,323.5 (773.92,422.1)

% of total air kerma

39.7 (29.157.3)

66.3 (55.777.1)

Acquisition air kerma

mGy

396.8 (257.0579.2)

712.5 (452.91,059.8)

% of total air kerma

60.3 (47.370.9)

33.7 (22.944.3)

* All p < 0.001; values are median (IQR)

The large relative change in air kerma rates between fluoroscopy and acquisition appears to be one of the more novel findings of this study. The investigators speculated that reasons for this may be multifactorial; for example, fluoroscopy entails low-dose radiation, which is more sensitive to tissue-based attenuation, and thus small changes in angulation can cause substantial change in the air kerma rate. Conversely, acquisition involves a large radiation dose to obtain higher-resolution images. In addition to beam angulation, body surface area emerged as a key secondary predictor of total air kerma rate.

Dr. Agarwal and colleagues found the principle of "as low as reasonably achievable" to be a reasonable goal for the cath lab: "It has increasingly become clearer that superior image quality at the expense of higher radiation is not necessary at all times, but enough definition in an image to accomplish safe and effective procedure with minimum radiation is an acceptable goal."

Using Lower-Rate Fluoroscopy: A Simple Solution?
In another study in the mini-focus issue of JACC: Cardiovascular Interventions, Eltigiani Abdelaal, MD, from the Quebec Heart-Lung Institute, and colleagues examined the impact of one simple change in reducing radiation exposure for patients and operators: lowering fluoroscopy rate. They did so in the setting of diagnostic coronary angiography (DCA) and PCI using the transradial approach (TRA). Although TRA offers lower rates of vascular and bleeding complications and improved patient comfort, it increases radiation exposure for patients and operators.

In this study, the researchers compared the efficacy of the conventional dose of 15 frames per second (FPS) to that with a lower rate of 7.5 FPS in 184 DCA patients and 179 PCI patients. The primary endpoints were operator radiation dose, patient radiation dose, and fluoroscopy time.

When stratified by procedure type (FIGURE), the effects remained significant for operators in both modalities and for patients undergoing DCA but not PCI. Total fluoroscopy times did not differ significantly between low- or conventional-rate fluoroscopy for either DCA or PCI; neither did procedural duration or contrast volume.

FIGURE. Effect of 7.5 FPS on Operator Radiation Dose and Patient DAP

Although use of low-rate fluoroscopy may not impact patient risk for a single procedure, the magnitude of reduction may be considerable for complex procedures or cumulative for repeat procedures. For clinicians, the ≥20% relative reduction in operator dose lops off ~6 years of radiation exposure over a 30-year careerclearly a substantial reduction in risk for fatal or nonfatal cancers for operators.

The researchers echoed the concerns of Dr. Agarwal's groupbalancing imaging resolution and quality with fluoroscopy and procedural timesbut, notably, there was no decline in imaging quality with lower-rate approaches.